A backup power supply (also sometimes called an uninterruptible power supply) is a power supply that keeps computer hardware/software, medical devices or other sensitive or important electronics operating in the event of a power outage. Most backup power supplies serve to keep the hardware and software running for a few minutes until the hardware may safely be shut down or until a backup generator or other power source resumes providing power. Backup power supplies typically operate on a chargeable battery that provides power when the main AC power fails, thus making sure that the power to the hardware or electronics is uninterrupted.
In the past, several different types of chargeable chemical batteries have been used in uninterruptible power supplies. For example, Lead Acid chargeable batteries typically last about 2-4 years depending on environmental conditions like temperature, cycle use, and other variables. Recently, Lithium Polymer chargeable batteries have entered the market but they have similar life expectancies. All of the known chemical batteries, however, in addition to short lifespans, suffer from several other drawbacks including susceptibility to changes in temperature and shock, as well as overcharging and discharging inefficiency. Chemical batteries require significant maintenance and are potentially damaging to the environment when disposed of because they contain toxic chemicals. Moreover, traditional chemical batteries operate in a very narrow voltage range. For example, a 12 volt battery typically operates within a 3 volt range from approximately 10.7 volts to approximately 12.7 volts. Once a battery gets below 10.7 volts, any energy stored in the battery is not usable and is lost.
The ultra capacitor is a relatively new device and offers a new way of storing electric energy. Instead of storing energy electrochemically, it stores it in an electric field. Ultra capacitors have multiple advantages over conventional batteries, including a lifetime of over 10 years, resistance to changes in temperature, shock, overcharging, and discharging efficiency. They require less maintenance than conventional batteries and are light on the environment when disposed because they lack toxic chemicals. Their energy, however, is retrieved in the form of a voltage which decreases as the ultra capacitor discharges. Although the stored energy is retrievable, the use of an ultra capacitor in a backup power supply has not been achievable because the coupled electrical devices require a constant voltage level which the ultra capacitor, by itself, cannot provide.
Accordingly, a need exists for an uninterruptible power supply that uses a power source in the form of an ultra capacitor along with an accompanying circuit that together, form a reliable uninterruptible power source for providing backup power in the form of a constant voltage level.